Thank you for that information Lykle. I think that I will most likely use concrete as epoxy is rather expensive if it needs it. I intend finishing it and testing it before I decide whether to fill it or not.

I like the idea of filling it with sand, I can get all I need for free off the beach!

Today I fitted the motor, I needed a mounting plate so I cast a flat plate 250x150x10mm. I'm getting hooked on casting.The mechanism for raising and lowering the knee took some thought. I have a worm gearbox that I thought would be good for turning the nut on an Acme thread leadscrew that I can buy. Unfortunately the gearbox ratio is 50:1 which would have entailed many thousands of turns of the handle to go from top to bottom. I decided to motorise it and as I already have a 1/2HP motor that was straight forward, even with the motor it will take three minutes to go from top to bottom. this shouldn't be a problem as I will normally be making relatively small adjustments in height.I have made it so that I can also use a handle for fine manual adjustment. One turn of the handle raises it 0.1mm which will give me very precise setting.Does anyone have a leadscrew of 25mm or 1" dia with a thread length of at least 500mm that they want to dispose of?

I think you will be much better off long term with pre-washed sand from a store than with salty beach sand. Agreement the first 2 or 3 years your machine's insides won't notice it. Eventually however the salt will find metal and atmospheric moisture and the fun will begin.

I am really curious to see how the knee joint plays out as far as slop and maintaining a specific height to a few thousandths goes.

I have been quiet for a while, that is not because I have been idle. I have been making slow progress but I may have to cast the head casting again. I relied on my memory when boring for the main bearing and managed to make it oversize. I could make a sleeve which would probably be cheaper but take a lot more time.Superc I'm not sure what you mean by the knee joint. If you mean the vertical slide I have already found a problem. I thought that I had adjusted it to the minimum slop but when I checked it yesterday I did find some movement in it. I think that I need to remove some of the paper shim that I have used. This is a major dismantling. I will do it when the leadscrew arrives as I will have to take it all apart to fit it.

Well yes, I meant the vertical feed. Looking at the original sketch, since I see only one screw raising the table, slop becomes a concern, especially if there is no way of firmly locking it in position. Second potential problem I see is what supports the sides of the table to keep the arrangement from rocking? Is there more than one 'angle plate' perhaps affixed to the table slides riding in grooves in the 'aluminum casting', or is there just one centrally affixed connection between the table and the main body?

The table slides on a 4" wide x 1/2" thick vertical runner. When it is set to height I will lock it with screws on the gib strip so I don't think that there will be any rocking. Fine height adjustment will be done with the dovetail slide on the head. More of a concern is forward sag, at present there is some movement but I am hoping to improve on that by adjusting the shims in the box slide. I will do that after I receive the Acme leadscrew as both jobs will require dismantling it to fit them and I don't want to have to do it twice.

The lead-screw for elevating the table is fitted. I connected it up temporarily and found that it operates very smoothly under power but when I tried to reverse it the motor got a bit smoky. Fortunately I turned it off quickly and now that it has cooled down it is still working, phew! Since that happened I have bought a reversing switch which I still have to sort out the wiring for. When the motor was running the wooden cabinet resonated, it was a bearable noise but I will try to make a resilient mount for the motor to try to quieten it.The table moves quite slowly under power so setting it accurately in position should be quite easy, I am also able to hand crank it for fine setting. The screw is fixed and the nut rotates around it. The height of the head can also adjusted precisely.I have obtained the main spindle and bearings and fitted them. It was an interesting piece of machining for the head casting. Firstly I bored it with it mounted on the cross-slide and the made a mandrel and turned the bearing recesses with it mounted between centres. The bearings are taper-roller, I also fitted oils seals top and bottom.

I am getting quite excited by my milling machine. From the beginning I have had doubts about the practicality of what I am trying to do. But, I was looking at it today and feel more confident that I am going to produce a machine that will be capable of producing accurate work. Any comments on what I have done so far?

I have a concern about concrete filling -- which may or may not be valid. Up to those with experience combining these two materials to say.

Portland cement is highly caustic and aluminum is particularly subject to attack by alkalis. Will this cause problems, not only during the filling stage, but also down the road? I think even cured concrete remains basic for quite a long time. With moisture from condensation (aluminum a great conductor, concrete much less so, and porous) I just wonder if problems like corrosion would cause either separation, or the opposite, expansion, or both in different places?

Could be I'm wrong -- hope so -- concrete would be a nice inexpensive vibration damping mass if not.

ps, I remember reading in an old ME about a large lathe built after the War out of concrete as the main material. And here in Vermont, at the Precision Museum in Windsor, there is a late constructed of marble (quarried here).

Thanks SMP. I have been reading, on another machining website, of problems that people have had with bubbles in their castings. There has been a discussion about the various degassing chemicals that can be used. I do not do any degassing, I just scrape off the slag and pour. I haven't noticed any bubbles in my castings. I am using mild steel for the crucibles, apparently that can cause problems with the castings. I haven't seen any problem with that either.Steve, I share your concern about using concrete as a filler. I rather like Andrew's idea of using lead shot, First I will finish the machine and try it out to see if it suffers from vibration and then decide what to do.

Apart from the chemical problems Al concrete, concrete shrinks, if you put it inside a tube, it will shrink away from the walls, having no damping effect! To use concrete effectively, it needs to be outside. If you make the bed out of concrete, with the reinforcing bars and sleeves to bolt the ways to you won't have any problems. Lead shot sounds much better than concrete.

I was thinking about the problem of concrete and it seems like there could be inexpensive solutions if cost was the determining factor.

Coating the inside of the aluminum with epoxy before doing the concrete pour would protect the aluminum, while using a relatively small amount of epoxy.

To deal with the shrinkage problem, there are a few possibilities -- one would be to use "hydraulic cement" which doesn't shrink.

Another would be to actually cast the concrete separately and just fasten it in place -- after all the rest of the machine is held together with fasteners. This would also allow you to remove it, if ever needed, which might be kind of handy. You might cast in pipe, or studs or nuts to facilitate fastening -- lots of different possibilities.